Method for additivating polymers in rotomoulding applications

1. A method comprising:

a) feeding into a microniser:

i) polymer fluff directly exiting a reactor; and additives comprising:

ii) phenolic antioxidant;

iii) organic phosphite or phosphonite antioxidant;

iv) anti-UV stabiliser;

v) optionally metal stearate;

vi) optionally densification aid; and

vii) optionally pigments; to form a dry blend

b) micronising the dry blend, while maintaining the dry blend at a temperature of from about 25°C. to at least 5° C. below the melting temperature of the polymer fluff, in order to obtain additivated polymer powder having an homogeneous size of from 10 to 1000 micrometres for rotomoulding;

c) retrieving the additivated polymer powder;

wherein no pre-treatment is performed prior to feeding the polymer fluff and the additives to the microniser, the pre-treatment that is used to add the additives to the polymer includes compounding, extrusion, use of solvent, or use of diluent.

2. The method of claim 1 wherein the polymer is polyethylene or polypropylene.

3. The method of claim 1 wherein the temperature in the microniser is maintained at a temperature that is at least 10 °C. below the melting temperature of the polymer.

4. The method of claim 1 wherein the phenolic antioxidant is octadecyl 3-(3′,5′-di-t-butyl-4-hydroxyphenyl)propionate, pentaerythrityl-tetrakis(3-(3′,5′-di-t-butyl-4-hydroxyphenyl)propionate, or a blend thereof.

5. The method of claim 1 wherein the organic phosphite or phosphonite is bis(2-methyl-4,6-bis(1,1-dimethylethyl)phenyl) phosphorous acid ethylester, tris-nonylphenyl phosphite, tetrakis-(2,4-di-t-butylphenyl)-4,4′-biphenylen-di-phosphonite, cyclic butylethyl propandiol, 2,4,6-tri-t-butylphenyl ester, or a blend thereof.

6. The method of claim 1 wherein the UV-stabiliser is a hindered amine light stabiliser.

7. The method of claim 1 wherein the dry blend comprises the metal stearate.

8. The method of claim 1 wherein the densification aid is present and is a mixture of a polyetherester as major component with a minor component selected from the group consisting of polyether-block co-polyamide, thermoplastic polyurethane, polyethylene glycol and fluoropolymer.

9. The method of claim 1 wherein the polymer is polyethylene having a density of from 0.920 to 0.965 g/cc and a melt index of from 0.5 to 25 dg/min.

10. The method of claim 1 wherein the polymer is polyethylene having a polydispersity index of from 2 to 10.

11. The method of claim 1 wherein the polymer is polyethylene, and wherein the energy consumed to micronise the polymer fluff is less than 60% of the energy consumed to micronise the pellets for the same polyethylene resin and under the same micronising conditions.

12. The method of claim 1 wherein the dry blend comprises the metal stearate, and wherein the metal stearate is zinc stearate or calcium stearate.

13. The method of claim 1 , wherein the additivated polymer powder is characterised in that it is free of solvent or diluent.

14. The method of claim 1 , wherein the method only includes one micronisation step.